Optical circuits typically include a group of individual and isolated optical elements that are arranged on a base, and that together perform an optical operation on a radiation beam or ray that passes through or is reflected by the optical elements. Each individual element is typically supported on the base by a mounting structure that may support a single optical element or a group of optical elements with respect to the base. It is customary that at least some of the individual mounting structures will include a capability for moving or adjusting a position of the optical element in one or more degrees of freedom at a final assembly step. The adjustments may be used to align individual elements along a common optical axis and to direct an output beam or ray from the optical circuit to a desired target location. Such alignments may also be used to direct back-reflections from optical surfaces away from the radiation source, e.g., a laser, so that the back-reflection do not affect the laser cavity output.
In many cases, alignment of the optical elements is so demanding that the optical elements cannot be oriented without adjustment, often to sub micron dimensions. Attempts to orient optical elements by simply machining or otherwise forming an optical element mounting surface to the tolerances required for pre-alignment of the optical element have not been satisfactory because tolerances achievable by metal forming techniques used to locate the optical element mounting surface fall far short of the tolerances that are routinely achievable using alignment and instrument feedback from, for example, a beam position detector.
For example, as shown in FIG. 1 a conventional frequency locker optical circuit includes a laser source 1, a lens 2, a first beam splitter 3, a second beam splitter 4, an etalon 5, a wavelength selective filter 6, a first detector 7, a second detector 8, and a controller 9. Generally, a small portion of the laser signal is passed through each of the etalon 5 and the filter 6 to determine the precise wavelength of the signal being output from the laser. If the laser needs to be adjusted, the controller 9 automatically adjusts the laser to return it to the desired frequency. As shown in FIG. 1 many, if not all, of the optical elements are adjustable with respect to the base in at least one and possibly three dimensions to ensure that the optical path is precisely aligned. This is critical, at least in part, due to the use of the etalon.
Etalons generally include a pair of optical surfaces that are separated from one another by a specific distance. The space or cavity between the optical surfaces may include any material transmissive and non-corrupting to the light transiting the gap, which may be solid, liquid or gas as in the case of air. Sealed etalons, which provide that the space between the optical surfaces is enclosed, may include trapped gas or vacuum or any desired pressure. If the etalon is slightly misaligned, its operational characteristics will completely change to a different frequency because the optical path length through the cavity will change. Optical circuits, therefore, that include etalons must be very precisely aligned to tolerances that far exceed assembly tolerances. Etalons may be used for a variety of optical applications, including variable wavelength filtering (by slightly rotating the etalon, changing its temperature, or otherwise varying the optical path on the cavity), optical filtering of certain wavelengths, and optical wavelength measuring systems. The precise alignment of the etalon in the optical circuit is critical and the fabrication of optical circuits using micro etalons remains time consuming and expensive.
It is known that conventional optics forming methods such as surface grinding and polishing, as well as well known optical surface measurement techniques such as using interferometers, can be employed to position optical surfaces to a much higher degree of accuracy than can be done by conventional metal forming techniques. Such optics forming methods and measurement techniques, however, are typically unsuitable for use in adjusting an optical element after the element is positioned on a base.
Optical circuits are utilized in many fields and are in wide use in laser systems, imaging systems, fiber optic communication systems and in optical disk devices such as compact disk memory, audio and video recording and playback systems. An optical circuit may include as few as two elements or may include tens of elements working together to perform individual optical operations. For example, a simple two element optical circuit may comprise a single surface of a flat glass plate having an optical coating thereon. In this case the optical coating may comprise an anti-reflection coating for performing a first optical operation and the glass having an index of refraction, which is different than air, performs a second optical operation on a beam passing through the glass.
Optical circuit examples may include beam isolators, a plurality of beam splitters in series, beam expanders, beam directing devices e.g. utilizing a plurality of individual mirrors, wave lockers used to select a laser output frequency etc.
There is a need therefore, for a system and method for fabricating optical circuits that are pre-aligned and pre-tested and require a minimum of alignment steps when installed in a larger optical system. Moreover, there is need to build and align such systems utilizing fabrication tolerances that are readily available by conventional optics fabrication techniques.
More recently, there is a need for optical circuits having miniature optical elements, especially for use in telecommunication systems utilizing fiber optics. In recent laser systems, beam diameters may range from about 0.01 mm near a work surface, to as large as 15.0 mm or more in other parts of the overall system. Accordingly, individual optical elements such as lenses, mirrors, beam splitters, prisms, filters, and the like, may only require an optical aperture in the range of about 1-15 mm in diameter. Moreover, it may be beneficial that the size of each individual element be, e.g. 1×1 mm to about 15×15 mm to reduce the size of the optical circuit or to reduce weight.
It is also a typical problem that individual miniature optical elements are difficult to fabricate, difficult to measure, difficult to handle, difficult to mechanically mount and align and difficult to coat with optical coatings. In fact individual optical elements are sometimes made larger than necessary because the larger elements can be made for less cost and are easier to manipulate. An example of a miniature optical element is disclosed in U.S. Pat. No. 6,276,806, which discloses a method of fabricating micro etalons (of about 10 mm by 10 mm by 10 mm) that may be used in a variety of optical circuits. Such micro etalons, however, require very delicate and precise handling in fabricating optical circuits, and still must be adjusted once mounted to a base. Also, the micro etalon fabrication techniques disclosed in U.S. Pat. No. 6,276,806, are not readily adaptable to the manufacture of sealed micro etalons. The manufacture of sealed micro etalons remains time consuming and expensive, requiring very small parts to be assembled in a controlled environment in which the desired gas and pressure are maintained in a controller fashion.
There is, therefore, a further need to provide systems and methods for fabricating miniature optical elements of high quality and low cost and weight.
There is also a need for a system and method for economically and efficiently fabricating a large number of optical circuits such as those containing micro etalons.
There is also a need for a system and method for economically and efficiently fabricating sealed micro etalons.
There is also a need for a system and method for economically and efficiently fabricating very precise micro etalons.